In a classical quadrupole mass spectrometer, molecules are bombarded by high energy electrons, resulting in the fragmentation of the molecular ions. These fragments are very similar to each other, where respective intensities can help to discriminate the original molecules through the use of a spectrum superposition technique.
In the case of mud gas logging, methane is a major contributor to the mud content. This gas is typically used as a chemical reagent for chemical ionization. At the spectrum level and in the presence of methane, a single peak contribution can come from electron ionization induced ions and chemically generated ions. With a large number of molecules, it can be difficult to reduce the uncertainty of the molecule composition in the original mud sample with the fragments originating from multiple molecules, even from isomers of these molecules.